The present invention relates to the field of fiber optics, particularly to an optical fiber/optical component assembly. The invention may find use in systems of data transmission via fiber optics channels, as well as in optical sensors based on the use of optical fibers, etc. The invention also relates to a method of manufacturing and assembling the aforementioned assembly.
In the field of fiber optical communication, an assembly of an optical fiber with an optical component is normally carried out through a coupler between an optical fiber used for transmission of optical signals and an optical system component, such as a light source, e.g., a laser diode. Such a coupler is an important part of the optical system. However, it should satisfy a number of technical requirements such as simplicity of manufacturing, assembling, and alignment procedures under mass production conditions.
In the past, several techniques have been utilized to align the optical fiber to the lens both in a longitudinal and transverse direction. Each of the techniques employed one of a plurality of lens contacts for terminating the optical fiber. A first of these techniques teaches that the lens contact is terminated by micropositioning a xe2x80x9cpigtailedxe2x80x9d optical fiber, that is, the fiber which is back illuminated and optimized in position. The optimized position of the fiber is accomplished by projecting the back illumination of the fiber through the lens to a target on a screen. When the back illumination through the lens strikes the target on the screen, the fiber is bonded securely and thus optimized in position with the fiber end face interfacing the focal point of the lens. A second of these alignment techniques involves providing a cylindrical hole behind the lens. The cylindrical hole is aligned along the optical axis of the lens and is blind ended at the focal point of the lens. Also, the cylindrical hole has a diameter that accommodates the optical fiber with a close fit, and the optical fiber is bonded within the cylindrical hole with an index of refraction matched adhesive.
The process of aligning the optical fiber to the lens requires achieving both forward alignment and lateral alignment of the optical fiber, which is usually a problem. In the first technique, the problem manifests itself in the tedious requirement of adjusting the optical fiber to a stringent tolerance to permit the back illumination through the lens to strike the target. A second problem that exists concerns the necessary use of an epoxy to affix the optical fiber to the lens. In the back illumination method, epoxy is required to securely bond the fiber to the lens. In the second technique of alignment utilizing the cylindrical hole in the lens, the epoxy produces a hydraulic effect when the fiber is inserted into the cylindrical hole. The epoxy which is an index of refraction matched adhesive creates a hydraulic force that prevents the fiber end face from reaching the focal point of the lens. This problem results in a loss of or attenuation of the optical signal.
Several prior-art references which are relevant to the instant invention have been discovered and will be discussed briefly.
British Pat. No. 1,017,354 issued to Contina discloses a system in which light is transmitted from one element to another so that the difference in cross-sections between the elements can be effected within a very short distance without loss of intensity. An optical system comprised of two bundles of optical fibers is arranged with one end of a first bundle facing one end of a second bundle and spaced apart therefrom. The ends of the two bundles are of different areas and a transparent body optically couples the two ends together. The transparent body has a reflecting surface, which is substantially ellipsoidal in shape and coaxial with the bundle ends. Light rays of the optical signal are reflected such that they pass through a focal point in an axial end face of the second bundle.
British Pat. No. 1,429,843 issued to Kahn discloses a coupling unit consisting of a first housing member and a second housing member, each carrying an end region of one of two light guides. The first housing member has a first coupling formed to fit into a second coupling of the second housing member. The first light guide is held centrally in the first coupling by a first body, and the second light guide is held centrally in the second coupling by a second body. During manufacture, the ends of the light guides may be polished with the faces of the first and second bodies. A lens is mounted between the ends of the two light guides. Accurate alignment between the lens and the light guide is required.
U.S. Pat. No. 3,950,075 issued to Cook, et al. discloses an optical communication system which includes a diode for emitting optical wave energy to be coupled to an optical waveguide bundle. A transparent spherical bead is axially aligned with the bundle and the center of the light emitting area of the diode. The bead is securely mounted in an aperture, which extends through one end of an insert within a housing. Precise alignment of the center of the bead along the axis of the aperture results from a force fit. The diode is disposed in the housing for proper alignment of the light emitting area of the diode with the bead. The end of the bundle is disposed in a termination ferrule having an aperture, the bundle being potted in the ferrule by a bonding material. The ferrule maintains the fiber bundle in a substantially parallel alignment. A problem is the high tolerance alignment required between the diode, the bead, and the bundle.
U.S. Pat. No. 4,102,559 issued to Hunzinger discloses an optical structure comprising two very thick piano-convex lenses with a common axis. The convex surfaces of the lenses face each other while a radiation source and an input face of a fiber are each disposed on one of the convex surfaces in the vicinity of the axis. The main feature of the device resides in the considerable thickness of the lenses relative to the radii of curvature of the dioptric faces. As a result, aberrations, in particular spherical aberrations, are reduced while the dimensions of the device are such as to enable easy construction and handling.
U.S. Pat. No. 4,147,402 issued to Chown discloses a process for manufacturing a lens termination for an optical fiber using laser machining to form a cavity, which centers the fiber in the termination. A plastic preform is provided comprising a tube member with a coaxial bore having one end closed by a lens at least the rearward portion of which comprises a plastic material. The bore and lens are arranged such that the base of the bore lies in the focal plane of the lens. Light is directed from a laser through the lens so as to focus the light onto the base of the bore thus evaporating a portion of the plastic material to form a cavity which, when the termination is in use, receives the bared end of a coated optical fiber. An index-matching adhesive is used to bond the fiber within the cavity which produces the previously described hydraulic force preventing the fiber end face from reaching the focal plane of the lens,
U.S. Pat. No. 4,183,618 issued to Rush et al. discloses an optical waveguide including a connector having a longitudinal bore in which an end of an optical waveguide is to be anchored, lens means for transmitting light from one end of the waveguide and defining a recess including a focal point of the lens means, and a housing in which the connector and lens means are mounted. The terminal also includes an elongate optical member having first and second ends with respective end faces, the first end of the elongate optical member extending partially through the connector and being anchored therein, and the second end of the elongate optical member being mounted in the recess in the lens means with its end face disposed at the focal point of the lens means. The connector includes means for maintaining the first end of the optical member and an end of an optical waveguide in alignment with one another.
U.S. Pat. No. 4,327,963 issued to Knoe et al. discloses a coupling element for an optical transmission system having a coupling element comprised of a convex lens with a refractive index. The refractive index is dependent on a radius xe2x80x9crxe2x80x9d of a shell in the lens. The coupling element further includes a holder through which a capillary extends. The convex lens, which is spherical, is affixed to an end of an optical fiber with the lens-fiber interface being enclosed within the capillary. The capillary is preferably circular cylindrical in shape and may rest in a V-shaped groove of a holder. A transparent coupling medium may be disposed between the lens and the fiber for light refraction purposes.
As can be seen from the description of the prior-art devices given above, a problem associated with tedious axial and lateral alignments in connection of the fibers to optical components or to each other still exists. Furthermore, in some prior-art devices the fixation of the fiber in the adjusted or aligned position is performed with the use of a glue in a blind hole, whereby the glue in a liquid state produces a hydraulic effect which makes it difficult to ensure final accurate positioning of the parts being interconnected. Moreover, none of the prior-art devices is suitable for mass production, as they require individual sequential alignment of each single fiber in assembling of optical fiber couplers.
U.S. Pat. No. 4,810,053 issued to Woith in 1989 relates to an alignment and retention device for optical transmission fibers having an optical lens with a forwardly directed curved surface molded to a rearward extension. The extension has an upper portion and a lower portion separated by a V-shaped gap, each portion having a longitudinally extending V-shaped groove for aligning and supporting an optical fiber. The lens and rearward extension are fashioned from a single piece of plastic with an abutment means comprised of a vertical stop at an interface therebetween. A focal point of the lens is located at the abutment means, and a retention means securely retains the optical lens while a clamping means surrounds the retention means forcing the upper and lower portions together for capturing the optical fiber within the V-shaped gap providing forward and lateral fiber alignment without using an index matching adhesive.
Although the device of U.S. Pat. No. 4,810,053 does not use an adhesive, it is extremely complicated in construction, has many miniature parts of complex shapes, involves time-consuming and multiple-step assembling, and is not suitable for mass production.
GB Patent 2,327,278 issued to Hiroshi Kanazawa discloses an optical fiber/laser diode assembly with a coupler between the fiber and the laser diode. The assembly is shown in FIG. 1. It has a laser diode 12 attached to a lens holder 11 that retains a coupling lens 13. The holder 11 is attached to an adjusting ring 16 for use in optical fiber multiport couplers.
Pending U.S. patent application Ser. No. 658619 filed by the same applicant in 2000 discloses an optical fiber coupler which is suitable for mass production due to self-alignment of optical elements during assembling and due to the butt connection of the end of the fiber with a flat end face of the lens element used as a reference surface. The axial and lateral alignment is achieved due to the manufacturing procedure that ensures strict planarity and parallelism of the mating end faces of the components, so that optical alignment is provided automatically as a result of assembling of the components into an integral coupling unit. However, the construction described in the aforementioned U.S. patent application relates to complicated optical systems with anamorphotic lenses the use of which is justified when a light source, such as a laser diode of the type, that has an essential difference in radiation characteristics in two mutually perpendicular axes (fast axis and slow axis), is used.
It is obvious that in coupling an optical fiber to a light source with distribution of light close to symmetrical, it would be more advantageous to use coupling structures less complicated than those described in the aforementioned U.S. patent application.
It is an object of the present invention to provide an optical fiber/optical component assembly with a coupler for coupling an optical fiber to an optical component, which is simple in construction, easy to align in assembling under conditions of mass production, and is suitable for use in optical fiber multiport couplers. Another object is to provide a method of manufacturing and assembling an optical fiber/optical component assembly, which is simple in construction and is suitable for mass production.